1. Field of the Invention
The present invention relates, generally, to a teeter lever for pneumatic cylinder/differential engine power-operated doors and, more particularly, to a removable teeter lever and removable gear for a pneumatic cylinder/differential engine for connecting an output shaft to connecting rods and, thence, to door panels of a mass transit vehicle.
2. Description of Related Art
Pneumatic cylinders have been utilized in mechanical systems to convert compressed air into linear reciprocating movement for opening and closing doors of passenger transportation vehicles. An example of this type of door actuating system is shown in U.S. Pat. No. 3,979,790.
Typically, pneumatic cylinders used in this environment consist of a cylindrical chamber, a piston and two end caps hermetically connected to the cylindrical chamber. The end caps have holes extending therethrough to allow the compressed air to flow into and out of the cylindrical chamber, to cause the piston to move in a linear direction, and to apply either an opening or closing force to the vehicle door.
Pneumatic cylinder/differential engine systems have also been designed for opening and closing doors of passenger transportation vehicles. Examples of these systems are shown in U.S. Pat. Nos. 4,231,192; 4,134,231; and 1,557,684.
As illustrated in FIG. 1, a known pneumatic differential engine consists of a large pneumatic cylinder 1 and a small pneumatic cylinder 2 attached to a housing 3. The large pneumatic cylinder 1 is closed at one end by a large cap 48. The small pneumatic cylinder 2 is closed at one end by a small cap 50. A large piston 4 and small piston 5 are installed inside of the cylinders 1 and 2, respectively. Pistons 4 and 5 are attached to the toothed rack 6 which is engaged with the gear 7. The gear 7 is permanently attached to the shaft 8, so that linear movement of the pistons 4 and 5 is converted into rotational movement of the output shaft 8. The teeter lever 9, as shown in FIG. 2, is welded to the end of the output shaft 8, and is connected by the rods 10, 11 and levers 12, 13 to the vertical shafts and arms linked to the vehicle door panels (not shown). As a result, rotational movement of the output shaft 8 causes rotational movement of the teeter lever 9 which causes opening and closing of the vehicle doors.
The small pneumatic cylinder 2 is constantly connected to a reservoir of compressed air, through opening 52 in small cap 50 so that a positive pressure is constantly applied to the surface 54 of the small piston 5 facing small cap 50. The large pneumatic cylinder 1 is connected to a three-way valve via opening 49, which provides connections to a source of compressed air during a door closing mode or to an exhaust member for exhausting the air from the large cylinder 1 during a door opening mode. The spring system 14 and sealing disk 15 provide cushioning of the movement of the large piston 4 at the end of the door opening stroke.
During a door closing mode, the air is admitted to large cylinder 1 through the three-way valve, as discussed above, and pressure is applied to the surface 56 of large piston 4 facing the large cap 48. Because of the difference in the surface area of large piston 4 and small piston 5, the application of air pressure within the large cylinder 1 causes the pistons 4 and 5 to move toward small cap 50 or to the right (as shown). Linear movement of the rack 6 is converted into counter-clockwise rotation of the gear 7 and output shaft 8 and, consequently, rotation of the teeter lever 9, which causes the doors to close.
During a door opening mode, the large cylinder 1 is connected to the exhaust valve of the three-way valve to allow the air in this large cylinder 1 to flow out due to pressure acting on the surface of the small piston 5 in small cylinder 2. As a result of this pressure differential, pistons 4 and 5 move toward large cap 48 or to the left (as shown), rotating the gear 7, shaft 8, and teeter lever 9 in the clockwise direction, as viewed in FIG. 1. The movement of the piston 4 toward the large cap 48 causes compression of the spring system 14, and linear movement of the sealing disk 15 toward a cushioning chamber 58.
Cushioning at the end of the door opening mode occurs as the disk 15 seals the exhaust opening 59 of cushioning chamber 58. The air flow out of the cylinder is restricted to a small orifice (not shown), slowing the movement of the pistons 4 and 5. This slowed movement allows the doors to continue opening at a slow speed (cushioning) until fully opened.
In the present engine design, the teeter lever 9 is welded to the output shaft 8 and the pinion gear 7 is secured to the output shaft by a roll pin inserted into a hole extending through the hub of the pinion gear and the shaft. This hole is drilled as a single operation with the pinion gear 7 already positioned on the welded shaft 8 and teeter lever 9 assembly. Once this hole is drilled, the pinion gear 7 and the welded shaft 8 and teeter lever 9 assembly become a matched set, inasmuch as the angular relationship of the teeter lever 9 to the pinion teeth determines the angular synchronization of the door panels to the position of the piston 4, and rack 6 assembly within the differential engine.
In order to remove the teeter lever 9 from the engine, the engine must be disassembled and the roll pin driven out of the gear 7 and the shaft 8 and teeter lever 9 assembly. If either the pinion gear 7 or the teeter lever 9 and shaft 8 assembly is damaged, all of these components must be replaced in order to restore the differential engine to operation.
It can be observed from the design of the existing differential engine, that replacement of either the teeter lever 9 or the pinion gear 7 requires that the entire mechanism be disassembled. Neither the pinion gear 7, nor the shaft 8 and teeter lever 9, are interchangeable. Consequently, these components must be replaced as a set. Moreover, the pneumatic differential engine, once assembled, becomes unique to a specific door configuration, and differential engines cannot usually be interchanged between different door configurations.
These factors impose both labor and material expense burdens upon the maintenance of door systems equipped with the present pneumatic differential engine.